The present invention generally relates to counted value storage methods and systems, and more particularly to a counted value storage method and system which store a counted value and is suited for storing counted values corresponding to a number of prints, rotation time of a motor, a current applying time and the like in an image forming apparatus such as a printer.
In an image forming apparatus such as a laser printer, a copying machine and a facsimile machine, counted values corresponding to a number of prints, rotation time of a motor, a current applying time and the like are stored in a non-volatile memory. For example, the non-volatile memory is a serial read/write electrically erasable programmable read only memory (EEPROM), and data related to the counted values are successively stored in one or a plurality of memory areas of the EEPROM using a pointer.
Generally, there is the limit to a number of times a write operation can be carried out in the EEPROM. When a 16-bit EEPROM is used, for example, a memory capacity of 10 words is required to count 100,000 when the EEPROM is limited to 10,000 write operations.
However, within one word which is made up of 16-bits, one horizontal parity bit is required to make a parity check for detecting a binary code error as shown in FIG. 1. As a result, a data part of one word is made up of 15bits, and a maximum number which can be described by this data part is 32768. In this case, it is impossible to count up to 100,000. For this reason, an upper word is conventionally provided to describe upper digits. In other words, lower words and an upper word are provided.
Accordingly, one lower word is used to count up to 10,000, and this lower word is then discarded. A next lower word is used to count up to another 10,000. The counting is carried out similarly thereafter, and ten lower words are used to count up to 100,000. For this reason, when an error is generated in the data which is counted when reading the data from the EEPROM, it is impossible to correct the error and the counting operation is stopped at this point or a new counting operation is started from this point. However, when starting the new counting operation, there is a problem in that the data of the counted value is no longer reliable.
On the other hand, according to the conventional counted value storage system, the pointer which indicates the write-in address of the next counted value must also be stored in the EEPROM. As a result, there is a problem in that the available memory capacity of the EEPROM becomes limited due to the necessity to store the pointer.